"Party time is 'pretty' time!"
-Holly Holden
With so many allergies prevalent these days, I believe it is thoughtful and prudent to repurpose place cards in a place card holder to indicate what is being served.
Cards and their holders are normally used to indicate where a guest is to be seated at dinner. I also use them to describe what is being served on a cocktail or a buffet table.
By naming what an item is on a place card positioned next to a respective platter, tray or chafing dish, it becomes an easy visual for your guests to see what something is! I do not write the list of ingredients, but simply label it as a "lobster dip" or "curry ball with pecans."
For other items on the table such as a smoked salmon, Smithfield Ham, or chilled shrimp, I think they are rather self-explanatory, so I do not feel the need to have a card describe them.
Before any event, I always explain to my serving staff the ingredients and the name of what they will be passing around. This way, they are informed and can answer any questions such as if there are nuts or dairy in case a guest inquires.
As a host or hostess, the onus is on you to make your guests feel at ease, and little details like this go a long way in showing that you care about them.